Method and apparatus for producing metal filaments



Sept. 22, 1959 w. WADE ETAL 2,904,859

' METHOD AND APPARATUS FOR PRODUCING METAL FILAMENTS Filed Feb. 16, 1956 strength and a casting surface of the contour needed. For purposes of illustration, the concavity of the surface 7 and the rotary casting surfaces of the modified apparatus described below is shown greatly exaggerated.

The essential improvement provided by this invention is the provision of a molten metal ejection device capable of discharging a plurality of streams of molten metal onto the recessed casting surface 7 whereby the spinning capacity of a single machine comprising one chill block may be greatly increased. For this purpose, a container or reservoir 10 is supported in a fixed position by means, such as a brace 11, over the chill block 4. When the apparatus is arranged and adjusted for producing uniform product, a plurality of nozzles 12 are aligned to cause the molten metal discharged from the orifices thereof to impinge upon the same circular portion of the surface 7. However, if it is desired to produce, for example, a filament of different character by each nozzle, then the nozzles may be aligned to deposit streams of molten metal upon different portions of the surface 7. This may be accomplished by variations in the settings of the nozzles While holding the container in a concentric position, or moving the container to a non-concentric position in which its axis is nonparallel to, or parallel but spaced from, the axis of rotation of block 4.

Molten metal may be fed to the container in such a manner as to maintain it safely above the lowest level for entering the nozzles 12 through a tube 14 connecting the container with a reservoir not shown. Pneumatic pressure is provided within the container 10 by means such as the tube 15 which connects the container to conventional gas pressure generating and regulating means not shown. If desired, the level of the liquid may be automatically maintained within the range provided by a pair of electrical terminals 16 and 17 connected with conventional control means for operating a valve in the metal supply system comprising the line 14. In the sectional view, Fig. 2, are illustrated the inside openings 19 of the nozzles 12. Although the means hereinabove described for forcing molten metal through the nozzles at a desired velocity is pneumatic, various other equivalent means are possible such as various types of pumping systems adapted for handling metals of relatively low melting points, such as one shown in Fig. 3 and described below.

In operation, molten metal that is ejected from the nozzles 12 as liquid streams impinge on the open surface 7 of the chill block 4 as a liquid. The angle at which liquid stream approaches the surface may be called the angle of incidence of approach. The super heat and latent heat of fusion is removed from the metal by intimate contact with said block; the metal is thus solidified. It remains in contact with the surface 7 for a short arcuate length a, e.g., one-half inch, and then is thrown free of the surface by centrifugal force in a direction taking an angle with respect to the casting surface 7 which may be called the angle of incidence of departure. The path or trajectory along which the product of each nozzle is discharged from the chill block remains substantially fixed as long as the spinning conditions and the position of the container 1!} are not changed. In the production of continuous filaments, continuity exists between the molten metal in the container 10, the molten metal in the air on its course to the surface 7, the liquid and solid metal on said surface, and the continuous filament leavmg said surface. In the production of staple filaments or powder, this continuity is interrupted as the product strikes the casting surface.

The manner in which the speeds of ejection and rotation of the chill block, and the several other variables which control the nature of the characteristics of the product which may be derived from a single nozzle, is discussed in detail in the above-noted patent. The following is an example of the basic process:

Employing an aluminum chill block having a diameter of 3", a weight of .6 lb. and a radius of curvature of 5", and having a surface finish of 30 microinches; and employing a glass round orifice having a diameter of 30p; molten tin having a surface tension of 526 dynes per cm. at ATs=50, was ejected at ft./sec. at a pressure of 6 lbs. The velocity of impingement was 300 ft./sec. and the angle of impingement was Filaments were produced having a length of 15 feet, a thickness of 10a and a width of 200p- Note.--The symbol ATs=50 signifies that the temperature of the metal at ejection was the melting temperature plus 50. a signifies microns.

Another arrangement by which a plurality of streams of molten metal may be discharged in continuous jet streams onto the casting surface is illustrated in Figs. 3 and 4 wherein the casting surface 7 of the chill block 4 receives a plurality of streams from nozzles 20 which extend through wall portions of a container 21. The container has a lowerlaterally extended portion 21a which provides a plurality of hollow projecting portions 21b, one for receiving each nozzle. An advantage of this arrangement for supporting the nozzles is that they may be aligned to discharge their streams in directions which are not directly radial as shown in the earlier described embodiment of Figs. 1 and 2. The streams discharged by the nozzles 20 in the presently described embodiment pass tangentially to a circle approximately concentric to the axis of rotation of block 4, such as when the container 21 is supported concentrically to the axis. As the ejection velocities of the metallic streams employed in this invention are considerable, this arrangement of nozzles is employed to avoid the direct addition of the kinetic energy carried in such streams to the centrifugal force supplied to the streams by the surface of the chill block on impingement therewith. Although the circle of tangency with the streams lies well within the circle of impingement on the surface 7, it is possible to build the container, and particularly portion 21a thereof, to such size as to direct streams of molten metal in a direction which is tangential with the circumference of impingement along the surface 7; however, such a container in practical application would be unduly bulky and be encumbered with problems of heat radiation and the maintenance of the temperature of the molten metal contained therein. The embodiment of Figs. 3 and 4 represents a compromise in design which effectively mitigates the addition of kinetic forces imparted to molten metal by ejection to centrifugal forces acting on the metal while in contact with the casting surface.

Also illustrated in the apparatus thus described, is a mechanical system for feeding the metal comprising a gear pump 23 in the feed line 24. For the production of filaments of uniform character the pump 23 is driven at constant speed by a chain 25 connecting it with the worm-gear drive 26 driven by a motor 27. The chill block 4 may be supported and driven in the manner illustrated in Fig. 1.

A simple modification of the apparatus illustrated in Figs. 3 and 4 is shown by fragmentary elevation in Fig. 5 wherein a container 30 for molten metal having a laterally enlarged lower drum-shaped portion 30a is sup ported concentrically with respect to the casting surface 7a of the chill block 4a. A peripheral wall of the drumshaped portion supports detachable adjustable hollow elbow fittings 32 in which are secured nozzles 33. The fittings 32 may be attached, as shown, in the manner of threaded pipe fittings to the container portion 30a. The cant of each fitting with respect to the container 30 is thereby independently adjustable to enable the path of discharge to be aligned toward the surface 7a as desired. A means for heating the container such as the flame burner 35, may be provided to maintain the metal stored therein at a desired temperature above its melting point. If desired, the temperature of the molten metal inside the container 30 may be controlled within a desired range by a thermostat 36 in contact with the molten metal, such thermostat being electrically connected to a solenoid valve 37 in the fuel line for the burner.

A further embodiment of the invention is illustrated in Fig. 6. Shown herein is the rotatable chill block 4 with a circular metal receiving cup 40 of circular transaxial cross-section secured at the bottom of the casting surface 7; the cup 40 is positioned coaxially with the block. The body of the cup comprises a high strength material, such as stainless steel. Supported within the recess of the cup 40 defined by the inner cylindrical surface 41 is an open-top cell 42 of heat resistant material, such as tungsten carbide. The opening of the cell at its top is circular and smaller in diameter than the diameter of a lower portion of the cell recess along the circumference of which apertures 43 are angularly spaced with respect to the axis of the chill block. Thus, the lateral surface defining the recess slopes from the top opening away from the axis of rotation toward the circumference along which the apertures 43 occur whereby during rotation of the block 4 and the cup 40, centrifugal force acts on molten metal in the cell 42 to trap it along the portions of the cell recess of larger diameter and to force it through the apertures. These apertures, referred to herein also as orifices, extend also through the lateral Wall of the cup 40. Supported above the cooling block is a reservoir 44 for feeding molten metal through a tube 45 extending downwardly therefrom into the recess of the cell. The amount of molten metal entering the cell 42 may be regulated by means such as a valve 46. Molten metal may flow from the container 44 by natural gravity, or a pressure system may be provided for supplying metal to the container and thence to the cell at a uniform rate as hereinbefore described with respect to other embodiments.

The system illustrated in Fig. 6 is characterized by impingement of streams of molten metal at fixed points rather than on circular areas of the surface 7, Le, when the conditions of spinning are held constant. Restriction of impingement to fixed points occurs because of the lack of relative rotation between the metal-discharging agency and the casting surface. Except for a slight deflection from a purely radial direction caused by windage within the region enclosed by surface 7, the molten metal, after deposition on the surface 7, proceeds a generally radial direction upwardly along the surface 7 until solidified, whereupon it flies off the surface in the form of staple fiber, varying downwardly from 2 inches in length to particles or flakes which are no longer than their width. This arrangement of the apparatus has as a primary advantage, mechanical simplicity of structure and operation. It is less satisfactory than other forms of apparatus described herein for continuous filament production. Collection of the product of apparatus illustrated in Fig. 6 must be provided along an entire circumference of the region surrounding the cooling block, since the agency for placing molten metal on the casting surface rotates therewith.

Fig. 7 illustrates another form of the invention in which the device for discharging molten metal upon the casting surface may be rotatable. In this instance a metal distributor comprising an outer shell 51 of high strength material, such as stainless steel and an inner casing 52 of heat-resistant non-alloyable material, such as tungsten carbide, is supported by the shaft 53 of a motor 54. Preferably the motor 54 is capable of being operated at any constant speed within a wide range of speeds of rotation. The parts of the distributor are built accurately circular and concentric with respect to the shaft 53 to provide as accurate dynamic balance as reasonably obtainable. Molten metal is supplied to the recess 55 of the distributor from a receptacle 57 through a tube 58 which extends into, or in immediate superposition with, the recess. The molten metal is fed into the recess at a rate in accordance with the rate of discharge from the distributor. As the-molten metal is forced from the distributor primarily by centrifugal force, the rate of discharge is dependent upon the speed of rotation of the distributor and the size and number of metal-discharging orifices or passageways 59 provided through the wall of the distributor. In using this apparatus, the distributor may be turned in the same direction as the chill block 4, or in the opposite direction. This form of apparatus is highly adapted for the formation of continuous filaments which are collected within a continuously circular region surrounding the apparatus shown.

In practicing the present invention, the rotary chill blocks, such as described in the foregoing description of the various apparatus modifications, have been satisfactorily constructed of stainless steel, aluminum and brass.

An important feature of the chilling or casting surface formed on the chill block is the finish thereof. Surfaces having finishes varying from about 1 to 50 microns, as checked with a profileometer, have been successfully used in producing the cast metal products of small cross-section herein referred to. In forming the chill block, the metals named and any other high strength metallic material capable of taking the polish desired, and which do not alloy with the molten metal to be spun, may be used. As to size, chill blocks found to be satisfactory in this invention varied from 3 inches to 7 inches in diameter, which was approximately the extreme diameter in each case of the casting surface formed thereon. The chill blocks were rotated at speeds up to 30,000 revolutions per minute to develop impingement velocities along predetermined circular areas within their perimeters of up to 1,000 feet per second. Orifice members, such as orifices 20 (Fig. 3) and orifices 12 (Fig. 1), were constructed of glass, silicon carbide, tungsten carbide and stainless steel. For operation at higher temperatures, i.e., for spinning filaments from the higher melting of the nonrefractory metals, the more heat resistant materials, such as silicon and tungsten carbides, provide orifices having greater service life. While metal products have been successfully produced from orifices having apertures in the range of 3 to 300 microns in diameter, a satisfactory aperture size which permits versatile variation of spinning conditions to obtain products having desired properties within a wide range, is about 30 microns. The rates of ejection therethrough may be varied substantially, e.g., from 25 to 300 feet per second, to correlate the ejection velocity of the nozzles to the speed of the chill block and the other variables to obtain a desired product.

While preferred embodiments of the invention have been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described our invention, we claim:

1. The method of transforming molten metal into solid molten metal products of extremely small cross-section comprising forcing molten metal from a common body thereof through a plurality of orifices onto a surface of revolution of concave re-entrant diametral cross-section, rotating a container of said body of metal at a given speed to apply centrifugal force to the metal to expell it through the orifices, rotating the surface at the same speed and collecting the molten metal as separate streams upon angularly spaced portions of said surface, said molten metal on contact with said surface being solidified and then urged from the surface by centrifugal force to form said products.

2. A device for casting solid metal products of extremely small cross-section comprising a chill block having a smooth polished open surface of revolution, the portion of said surface for receiving molten metal being produced by a generatrix which extends away from the axis of rotation at an angle less than a right angle, hollow means fixedly mounted on said chill surface and disposed centrally of said surface about said axis for receiving molten metal, said hollow means having orifices spaced radially-fromits axisand angularlythereaboutfor discharging separate streams of molten'metal upon selected areas-of said surface, and means for rotating said chill block and said'hollow means at the same speed so as to force the molten metal from said hollow body at high velocity against the chill surface whereby the molten metal is'solidified and urged from the surface 'by centrifugal force to form said products.

"3. :Adevice for casting solid metal products of extremely small cross-section comprising a chillblock having a-srnooth polished open concave surface having the radius of curvaturethereof on an axis of rotation with the surface extending concentrically about said axis, hollow 'means fixedly mounted on said chill surface and disposed centrally with respect to said surface and its axis 'for'receiving molten metal, said hollow means having orifices spaced radially from said axis and disposed in 'angularly spaced arrangement'thereabout for discharging small streams of molten metal onto selected areas of said surface and means for rotating said chill block and said hollowmeans at the same speed'for forcing the molten metal from said hollow means through said orifices at high velocity whereby the molten metal .is solidified and urged from the surface'by centrifugal'force to form said products.

References Cited in the file of this-patent UNITED STATES PATENTS 809,671 CoWing Jan. 9, 1906 950,884 Winner ,Mar. 1, 1910 989,075 Staples Apr. 11, 1911 1,291,603 Nagy Jan. 14, 1919 1,592,140 Horton et al. July 13, 1926 2,062,093 Kann Nov. 24, 1936 2,318,244 McClure May 4, 1943 2,752,196 Chisholm et al June 26, 1956 2,793,395 Richardson May 28, 1957 FOREIGN PATENTS 904,048 France Feb. '12, 1945 

